Recently, as an Internet protocol television (IPTV) industry has been expanded, a technique of inserting and extracting information for tracking pirates, who make duplicate copies illegally, from a terminal in real time has been drawing great attention. That is because that an analog display and a digital display coexist in the present service environment and because that in case of transferring image data through an analog interface, there is no definite secure transmission standard. Actually, when video data is transferred through an analog interface, it is possible to capture standard grade images. Recently, an apparatus for capturing such images is cheap enough for anyone to buy one. Accordingly, there has been used various watermarking techniques for tracking an illegal distribution of contents. Generally, if the inserted tracking information is found by a user when image data is reproduced, it may arouse the user's antipathy. Therefore, as a watermarking technique for tracking pirates, there has been mainly used a method of processing data and inserting it into a specific portion of video data so as not to stand out. In particular, a watermarking method of inserting tracking information in an invisible form into image data requires a complex operation depending on an algorithm by image frame.
A set-top box is a dedicated device that turns an external input signal into content to be outputted through a display device. For example, an IP set-top box is a dedicated device that turns various kinds of image signals transmitted through an Internet protocol into contents to be outputted through a TV monitor for offering an IPTV service. In the IP set-top box, image processes, such as parsing, decoding, mixing and output, of image signals of contents and an EPG (Electronic Program Guide) image are implemented in hardware and applications are driven by using a predetermined CPU.
However, since the IP set-top box has limited function, it is difficult to perform various operations. Particularly, without using a dedicated SoC (System on a Chip) including a watermarking algorithm, it is difficult to perform a complex operation related to a watermarking technique.
Further, as a method of inserting tracking information into video data, there is a method of overlaying images containing the tracking information with decoded image information before being outputted through a TV monitor. Since the overlay is implemented in hardware such as a decoder, if such a method is used, a watermarking function can be effectively implemented with little need of operations in a CPU. However, in this case, the image containing the tracking information is directly exposed to a user, and thus, it may be vulnerable to various attacks such as rotation, translation, cropping, scaling, frame rate conversion, and resolution conversion.
Further, in case of detecting tracking information from illegally distributed contents, if there is any error in the detected tracking information, the whole tracking information should be detected again. Therefore, it has taken a lot of time to detect the tracking information.
As one of prior arts, there has been disclosed Korean Patent No. 10-0405827 entitled “Method of inserting/extracting digital watermarks and apparatus for using thereof.”
This prior art relates to a watermarking technique in which image data such as a logo and a picture is inserted into an video data as a watermark, and a watermark contained in the video data is extracted so as to be identified visually. Further, this prior art discloses a method of preventing a duplicate insertion of a watermark by measuring a correlation between the digital watermark inserted into the video data and the generated digital watermark.
However, in accordance with this prior art, the apparatus of inserting a watermark is required to excessively perform operations, and, thus, it is not suitable for an apparatus with low specifications. Further, if there is any error in watermarked information, the whole information should be detected again, and, thus, detecting tracking information is not effective.